Quasiparticle Interference, Quasiparticle Interactions, and the Origin of the Charge Density Wave in2H−NbSe2

Abstract

We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe 2 , that we measure by scanning tunneling spectroscopic imaging. We show from the momentum and energy dependence of the quasiparticle interference that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe 2 . We demonstrate that by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wavevector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions.In 2H-NbSe 2 , we use this combination to show that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the CDW ordering wave vector.

Temperature-driven topological transition in 1T'-MoTe2

“…Real-space interference patterns and their Fourier transforms will show intensity only at values of q allowed by the band structure at each energy. [64][65][66] Additional selection rules that govern the relative intensities for different q can exist due to crystal and time-reversal symmetry conservation laws, 63 structure of the scattering potential, 66,67 or matrix elements. In our experiments, we consider the impurities giving rise to scattering processes to be largely nonmagnetic, as observed for other transition-metal dichalcogenides.…”

“…In our experiments, we consider the impurities giving rise to scattering processes to be largely nonmagnetic, as observed for other transition-metal dichalcogenides. 66 To compute the expected QPI pattern at every energy, we calculate the spin-conserved scattering probability…”

Quasiparticle energy bands and Fermi surfaces of monolayer NbSe2

“…Among metallic TMDs, the stacked trigonal prismatic structure of niobium diselenide (2H-NbSe 2 ) is one of the most studied materials and an ideal system to study phase transitions as functions of temperature and dopings. It has been known for a long time 32,33 that threedimensional stacking structure of 2H-NbSe 2 is metallic at room temperature and undergoes a CDW transition at 33 K before becoming a superconductor 34,35 at 7.2 K although there has been the controversy regarding on the origin of CDW and the competition between CDW and superconducting (SC) states 32,33,[36][37][38][39][40][41][42][43][44][45] . After a few earlier attempts to investigate physical properties of its thin flakes 1,46,47 , a couple of recent works have reported successful isolations of its single layer form on top of various substrates and measure their CDW and SC phase transitions [27][28][29][30][31] .…”

Charge density waves and phonon-electron coupling inZrTe3

“…In this line of thinking, it is only natural to recognize the essential role of phonon-electron coupling in the formation of CDW order, as suggested by several authors [30,32]. This idea has been explicitly tested in quasi-2D materials both theoretically [29,[33][34][35][36] and experimentally [36][37][38], and has proved quite successful in explaining the q cdw that deviates from q n . In quasi-1D materials, the importance of phonon-electron coupling relative to that of FSN has remained largely untested, as the good agreement between q n and q cdw in 1D cases might appear to render such tests unnecessary.…”